1. Field of the Invention
The present invention relates to an electric motor driven compressor adapted to be used as a refrigerant compressor in an automotive air conditioning system or, in particular, to an electric motor driven compressor suitable for CO.sub.2 as a refrigerant.
2. Description of the Related Art
In an air conditioning system for an electric motor driven vehicle such as an electric car or a home-use air conditioning system, it has been general practice to use freon gas, such as R134a or the like, as a refrigerant for the refrigeration cycle. Also, a refrigerant compressor used for compressing the refrigerant in the refrigeration cycle of these air conditioning systems is disclosed in JP-A-65580, for example, as what is called the "electric motor driven compressor" in which a motor portion and a compressor portion including a scroll-type compressor are integrally built in a common hermetic casing.
In the electric motor driven compressor, an intake chamber and a discharge chamber or other chambers are formed in the internal space of a casing in which the motor portion is arranged. If it is assumed that an intake chamber is formed in the internal spacing of the motor casing of an electric motor driven compressor of a conventional air conditioning system using the refrigeration cycle with the freon gas or the like as a refrigerant, generally, in the refrigeration cycle in which a flexible pipe such as a rubber hose is not used, the body or the like parts of the automotive vehicle are liable to develop noises and vibrations due to the effect of the discharge pulsation of the compressor unless the discharge chamber of the electric motor driven compressor has a sufficiently large capacity. The result would be an increased bulk of the pump portion, and a larger capacity of the discharge chamber would result in an increased bulk of the electric motor driven compressor as a whole.
In the case where the internal spacing of the motor casing is used as a discharge chamber, on the other hand, the motor casing is regarded as a pressure vessel, and therefore, a high pressure resistance value is required according to the law and regulations. Therefore, the thickness of the motor casing is required to be increased. The problem in this case is that the electric motor driven compressor would become not only bulky but also heavy. Further, in the case where carbon dioxide (CO.sub.2) is used as a refrigerant, the operating pressure, i.e. the discharge pressure of the refrigerant compressor is about ten times as high as that for a freon refrigerant. This problem is therefore not negligible.